The overall long-term objectives of this research are to elucidate mechanisms by which cell surface metalloproteinases and their secreted counterparts are regulated and interact, activate and degrade peptides and other proteins at the cell surface, as well as to define the physiological and pathological roles of these proteases in diseases such as diabetes mellitus and cancer. My approach has been to identify and characterize cell-associated proteinases and mechanisms used by living systems to degrade proteins and peptides according to the metabolic needs of the organism. The work has led to the discovery of meprins, unique mammalian metalloproteinases, and has provided fundamental information about the activity, structural characteristics, expression patterns, genes, and factors that determine secretion, retention in the endoplasmic reticulum, or proteasomal degradation of these complex and highly regulated enzymes. Our hypothesis is that meprins have a role in processing biologically active molecules such as gastrin and cholecystokinin, as well as cell-associated and extracellular proteins (membrane proteins, extracellular matrix proteins, and chemokines). In the next period, it is proposed to: (1) determine the physiological and pathological consequences of disrupting the meprin beta gene in mice, (2) disrupt the meprin alpha gene, and produce knockout mice for this subunit and double knockout mice for the alpha/beta genes, (3) define further physiological substrates for meprin mouse and human isoforms and the effects of metalloproteinase inhibitors, and to design potent inhibitors, and (4) determine structural factors critical for oligomerization and for enzymatic activity against polypeptides. The development of the meprin beta knockout mouse has provided a unique resource for the investigation of renal and intestinal disease. The multidomain, oligomeric meprin proteins provide a fascinating system to investigate regulation and activity of metalloproteinases that act at or near the cell surface. The studies will establish functions of meprins in developing, young and mature mice, and in cancer, inflammation and renal disease, and factors critical to regulating the enzymes.